<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<script type="text/javascript">
    let a;
    let b, c, d;
    let f = 521, g = 'adfa', h = [];


    function f1() {
        var v1 = 12; // f1外不能调用v1
    }

    var v2 = 1;
    var v2 = 2;
    console.log(v2); // 2

    {
        var v3 = 13;
    }
    console.log(v3); // 13

</script>
</html>